mm-drop-oom-code-from-exit_mmap.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Sep 27, 2022

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Andrew Morton

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2022-09-27 02:55 UTC #0 lore raw

The quilt patch titled
Subject: mm: drop oom code from exit_mmap
has been removed from the -mm tree. Its filename was
mm-drop-oom-code-from-exit_mmap.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Suren Baghdasaryan <[email protected]>
Subject: mm: drop oom code from exit_mmap
Date: Tue, 31 May 2022 15:30:59 -0700

The primary reason to invoke the oom reaper from the exit_mmap path used to be a prevention of an excessive oom killing if the oom victim exit races with the oom reaper (see [1] for more details). The invocation has moved around since then because of the interaction with the munlock logic but the underlying reason has remained the same (see [2]).

Munlock code is no longer a problem since [3] and there shouldn't be any blocking operation before the memory is unmapped by exit_mmap so the oom reaper invocation can be dropped. The unmapping part can be done with the non-exclusive mmap_sem and the exclusive one is only required when page tables are freed.

Remove the oom_reaper from exit_mmap which will make the code easier to read. This is really unlikely to make any observable difference although some microbenchmarks could benefit from one less branch that needs to be evaluated even though it almost never is true.

[1] 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
[2] 27ae357fa82b ("mm, oom: fix concurrent munlock and oom reaper unmap, v3")
[3] a213e5cf71cb ("mm/munlock: delete munlock_vma_pages_all(), allow oomreap")

[[email protected]: restore Suren's mmap_read_lock() optimization]

Link https://lkml.kernel.org/r/[email protected] open here

Signed-off-by Suren Baghdasaryan <[email protected]>

Acked-by Michal Hocko <[email protected]>

Cc Andrea Arcangeli <[email protected]>

Cc Christian Brauner (Microsoft) <[email protected]>

Cc Christoph Hellwig <[email protected]>

Cc David Hildenbrand <[email protected]>

Cc David Rientjes <[email protected]>

Cc Jann Horn <[email protected]>

Cc Johannes Weiner <[email protected]>

Cc John Hubbard <[email protected]>

Cc "Kirill A . Shutemov" <[email protected]>

Cc Liam Howlett <[email protected]>

Cc Matthew Wilcox <[email protected]>

Cc Minchan Kim <[email protected]>

Cc Oleg Nesterov <[email protected]>

Cc Peter Xu <[email protected]>

Cc Roman Gushchin <[email protected]>

Cc Shakeel Butt <[email protected]>

Cc Shuah Khan <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

---

 include/linux/oom.h |    2 --
 mm/mmap.c           |   30 +++++++++++-------------------
 mm/oom_kill.c       |    2 +-
 3 files changed, 12 insertions(+), 22 deletions(-)

include/linux/oom.h renamed from include/linux/oom.h~mm-drop-oom-code-from-exit_mmap +0 -2

@@ -106,8 +106,6 @@ static inline vm_fault_t check_stable_ad
 	return 0;
 }
 
-bool __oom_reap_task_mm(struct mm_struct *mm);
-
 long oom_badness(struct task_struct *p,
 		unsigned long totalpages);

mm/mmap.c renamed from mm/mmap.c~mm-drop-oom-code-from-exit_mmap +11 ~~-19~~

@@ -3085,30 +3085,13 @@ void exit_mmap(struct mm_struct *mm)
 	/* mm's last user has gone, and its about to be pulled down */
 	mmu_notifier_release(mm);
 
-	if (unlikely(mm_is_oom_victim(mm))) {
-		/*
-		 * Manually reap the mm to free as much memory as possible.
-		 * Then, as the oom reaper does, set MMF_OOM_SKIP to disregard
-		 * this mm from further consideration.  Taking mm->mmap_lock for
-		 * write after setting MMF_OOM_SKIP will guarantee that the oom
-		 * reaper will not run on this mm again after mmap_lock is
-		 * dropped.
-		 *
-		 * Nothing can be holding mm->mmap_lock here and the above call
-		 * to mmu_notifier_release(mm) ensures mmu notifier callbacks in
-		 * __oom_reap_task_mm() will not block.
-		 */
-		(void)__oom_reap_task_mm(mm);
-		set_bit(MMF_OOM_SKIP, &mm->flags);
-	}
-
-	mmap_write_lock(mm);
+	mmap_read_lock(mm);
 	arch_exit_mmap(mm);
 
 	vma = mas_find(&mas, ULONG_MAX);
 	if (!vma) {
 		/* Can happen if dup_mmap() received an OOM */
-		mmap_write_unlock(mm);
+		mmap_read_unlock(mm);
 		return;
 	}

@@ -3118,6 +3101,15 @@ void exit_mmap(struct mm_struct *mm)
 	/* update_hiwater_rss(mm) here? but nobody should be looking */
 	/* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
 	unmap_vmas(&tlb, &mm->mm_mt, vma, 0, ULONG_MAX);
+	mmap_read_unlock(mm);
+
+	/*
+	 * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
+	 * because the memory has been already freed. Do not bother checking
+	 * mm_is_oom_victim because setting a bit unconditionally is cheaper.
+	 */
+	set_bit(MMF_OOM_SKIP, &mm->flags);
+	mmap_write_lock(mm);
 	free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS,
 		      USER_PGTABLES_CEILING);
 	tlb_finish_mmu(&tlb);

mm/oom_kill.c renamed from mm/oom_kill.c~mm-drop-oom-code-from-exit_mmap +1 -1

@@ -509,7 +509,7 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reape
 static struct task_struct *oom_reaper_list;
 static DEFINE_SPINLOCK(oom_reaper_lock);
 
-bool __oom_reap_task_mm(struct mm_struct *mm)
+static bool __oom_reap_task_mm(struct mm_struct *mm)
 {
 	struct vm_area_struct *vma;
 	bool ret = true;

Patches currently in -mm which might be from [email protected] are